The present invention relates in general to a method and system for operating a camless internal combustion engine. More particularly, the invention relates to a method and system starting a camless internal combustion engine.
Conventional starting systems for cam-based internal combustion engines typically include an ignition switch, a battery, a solenoid and a starter motor. When the ignition switch is turned to the ignition or start position, an electrical circuit is completed between the starter motor and the battery via the solenoid and current is supplied to the starter motor. The starter motor, which is mechanically coupled to the crankshaft, is used to crank the engine until the combustion process begins.
The cranking process, however, typically involves the turning of camshafts and actuation of corresponding intake and exhaust valves. As such, because the valves are actuated, the starter may have to crank through one or more compression strokes of the various cylinders prior to the actual start of the combustion process. This results in additional mechanical work required for engine start-up, and as such, an increased amount of required electrical power from the starting system. The required electrical power is often much more than what is necessary to actually start the engine.
The inventor""s of the method and system described herein have recognized an advantage of using camless internal combustion engines to minimize the amount of electrical energy required for engine start-up. Camless internal combustion engines feature electronically-actuated valves which can be operated to provide variability in valve timing, duration and lift for each of valves. The valves are typically actuated using electromechanical or electrohydraulic actuators, and as such can be actuated as a function of one or more engine parameters such as speed, demanded engine torque or crankshaft angular position, to achieve optimal or desired engine performance. The inventors have recognized the advantage of valve timing, duration and lift variability as applied to optimizing the engine start-up process of a camless internal combustion engine.
The aforedescribed limitations and inadequacies of conventional engine startup methods and systems are substantially overcome by the present invention, in which a primary object is to provide a method and system for starting a camless internal combustion engine while minimizing the amount of electrical energy required for engine start-up.
The above object is achieved by a method for starting a camless internal combustion engine in response to a start signal, wherein the internal combustion engine includes a crankshaft and multiple cylinders each having one or more actuators for electronically actuating corresponding intake and exhaust valves. The internal combustion engine is mechanically coupled via the crankshaft to a starter motor, and the starter motor in turn is activated in response to the start signal. The method includes the steps of: positioning each of the valves in accordance with a predetermined valve initial position, wherein the valves are positioned so as to allow the flow of air in and out of each of the cylinders; rotating the crankshaft via the starter to a target idle speed for the engine; activating each of the valves in accordance with a predetermined valve activation sequence when the rotational speed of the crankshaft equals or exceeds the target idle speed; and activating each of the cylinders in accordance with a predetermined cylinder activation sequence after the valves have been activated.
An advantage of the above method is that by setting the valves to an initial position that allows for air flow in and out of cylinders, the amount of mechanical work required from the starter to crank the engine is substantially reduced. Additionally, because valve operation is delayed until the engine is cranked to the target idle speed, further mechanical work is avoided until a time the combustion process can be most optimally started. Accordingly, because the amount of required mechanical work is reduced, the electrical requirements of the starting system are reduced.
In accordance with another aspect of the present invention, a corresponding system for starting a camless internal combustion is provided, the system including: a start switch for generating a start signal; a starter motor mechanically coupled to the crankshaft for rotating the crankshaft to a target idle speed, the starter motor being activated in response to the start signal; a sensor for indicating the speed of the rotating crankshaft; and an engine controller coupled to the sensor for monitoring the rotational speed of the crankshaft and to the start switch for sensing the occurrence or presence of the start signal . The engine controller further provides valve initialization control signals to position each of the valves in accordance with a predetermined valve initial position, the valves for each of the cylinders being positioned so as to allow the flow of air in and out of each of the cylinders. Valve activation control signals are also provided by the engine controller to each of the valves when the rotational speed of the crankshaft equals or exceeds the target idle speed, and for activating each of the cylinders after the valves have been activated.
Still further, in accordance with yet another aspect of the present invention, an article of manufacture is provided for starting a camless internal combustion engine in response to a start signal, the internal combustion engine having a crankshaft and multiple cylinders each having one or more actuators for electronically actuating corresponding intake and exhaust valves. As previously described, the internal combustion engine is mechanically coupled via the crankshaft to a starter motor, the starter motor being activated in response to the start signal. The article of manufacture includes: a computer usable medium and a computer readable program code embodied in the computer usable medium for directing the computer to perform the steps of: monitoring the rotational speed of the crankshaft and for sensing the start signal; providing valve initialization control signals to position each of the valves in accordance with a predetermined valve initial position, the valves for each of the cylinders being positioned so as to allow the flow of air in and out of each of the cylinders; providing valve activation control signals to each of the valves when the rotational speed of the crankshaft equals or exceeds the target idle speed; and activating each of the cylinders after the valves have been activated.
Further objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying figures showing illustrative embodiments of the invention.